In general terms, a low NOx burner for combustion of particulate carbonaceous fuel may comprise a number of components, which may include:                a primary conduit to supply the pulverous fuel and a conveying gas which may be a comburant gas (often known as “primary” air);        a number of channels arranged for example concentrically around the pulverous fuel supply, through which comburant gas and other gas is supplied; in a low NOx burner there will typically be two or more channels for the combustion air or other comburant gas and these are often known as “secondary” air, “tertiary” air, etc;        devices to induce a swirling motion into the gas flows for example in the secondary and tertiary (etc.) channels;        devices to stabilise the flame, often placed on the end of the fuel supply pipe and sometimes known as the “flame-holder”;        devices placed inside the fuel supply pipe to control the fuel distribution at the outlet of that pipe;        supplementary equipment, such as igniters, light-up burners, flame monitoring sensors, etc., optionally installed in a separate tube, which may be located centrally within the fuel pipe where it is known as the “core” tube; the core tube may have its own air or other gas supply; alternatively supplementary equipment may be installed in other locations in the burner or close by.        
Where “air” is used herein both with reference to the prior art and with reference to the invention the skilled person will readily appreciate that other oxygen containing comburant gases and mixtures may be substituted in the familiar way for example for oxyfuel firing including a comburant gas having a reduced nitrogen content relative to air, for example comprising mixtures of pure oxygen and/or recycled flue gas and/or air. References to a comburant gas will be understood to include mixtures of gases including gases capable of supporting combustion and other gases.
It is known by those knowledgeable in this area that there are a number of variant low NOx burner designs available. Implicit in the design of any low NOx burner is the requirement to ensure that there must be sufficient oxidant in any oxidant/fuel mix to support the combustion of the fuel and to maintain the stability of the flame.